This invention relates to the field of insulated couplings for drill collars. More particularly, this invention relates to an insulated drill collar coupling and the method of manufacture thereof, wherein the threads of the coupling joint are coated with a layer of insulating material to effect electrical isolation between adjacent sections of a drill collar to prevent a flow of electrical current axially along the drill collar.
In the field of borehole drilling, there are several reasons for which it may be desirable to provide electrical isolation between adjacent segments of a drill collar. One of the principal reasons for wanting to electrically isolate adjacent sections of a drill collar is for the purpose of using the drill string as an electrical conduit for the transmission to the surface of data collected at the bottom of the well during the course of drilling. This concept of electrical telemetry has been known for many years, but it has not been applied on a serious commercial basis because of a number of problems. One of the principal problems involves the inability to produce a suitable insulated joint to provide electrical isolation between adjacent segments of the drill collar without seriously compromising the structural integrity of the drill collar. Typically, insulated joints heretofore known in the art have had a number of serious deficiencies or drawbacks, principal among which is the inability to withstand the stresses caused by torque loads in assembling and using the drill string.
Insulated joints of one kind or another are shown in a number of issued U.S. patents. While not intending to present an exhaustive list, typical prior art insulated joints are shown in U.S. Pat. Nos. 3,150,321, 2,940,787, 2,917,704, 2,388,141, 2,313,384, 2,300,823 and 1,859,311.